Global positioning system (GPS) navigational systems are often used by military and civilian naval, ground, and airborne vehicles for navigation. GPS receiver units receive positioning signals from a constellation of 24 Navistar satellites deployed in 12-hour orbits about earth and dispersed in six orbital planes at an altitude of 2,200 kilometers. The satellites continuously emit electronic GPS signals (or telemetry) for reception by ground, airborne, or naval receiver units. By receiving GPS signals from four or more satellites, a properly configured receiver unit can accurately determine its position in three dimensions (e.g., longitude, latitude, and altitude).
GPS navigational systems have tremendous benefits over other positioning systems in that these systems do not rely upon visual, magnetic, or other points of reference. However, conventional GPS navigational systems can experience blackout areas or regions when line-of-site is broken with the satellites. Some GPS navigational systems or other navigational systems in use today are nonfunctional in many areas due to signal blockage. For example, personal navigational systems often experience loss of signal when they are operated indoors, in dense urban environments (e.g., urban canyon), next to large buildings, underground, or in other blackout areas. Additionally recent attempts at augmenting GPS for this coverage deficiency has had mixed success and not resulted in a low cost worldwide solution. Additionally, approaches for resolving location through the novel use of cellular phone infrastructures does not currently provide reliable or sufficient discrimination for resolving occupied floor level within a multi-story concrete and metal building. Similarly, the approach of using GPS pseudolites does not solve all coverage problems due to inherent signal distortion, reflection and attenuation again brought on by the use of concrete and metal in many buildings. Furthermore the payback incentives are not clear, resulting in questions of who should pay for the new infrastructure, undermining solution standardization and widespread system implementation and coverage.
Thus, there is a need for a navigational system which not only is less susceptible to blackout areas, but is inherently low cost and having characteristics attracting widespread or worldwide infrastructure support. Further still, there is a need for a low-cost personal location system which can be utilized to determine position indoors. Even further still, there is a need to extend satellite navigation systems so they can be used indoors and in urban canyon environments.